1. Field of the Invention
The present invention relates to an electrostatic precipitator which makes it easy to improve the dust collecting efficiency.
2. Description of Prior Art
An electrostatic precipitator generates corona discharge between both electrodes of a discharge electrode and a dust collecting electrode by applying a high voltage between the discharge electrode and the dust collecting electrode producing a non-uniform electric field in the air so as to ionize the air in a portion where the electric field is intense, thereby to generate a charged zone. The principle of electrostatic precipitation is such that particles of dust and miscellaneous bacteria contained in gas to be treated are charged by flowing the gas to be treated through the charged zone produced between both electrodes of the discharge electrode and the dust collecting electrode, so that these charged particles are made to stick to the dust collecting electrode at an opposite potential so as to be collected.
FIG. 7 is a plan view of a principal part showing an embodiment of an electrostatic precipitator which has been heretofore used in general. In FIG. 7, the dust collecting section is composed of plate-shaped dust collecting electrodes 30a and 30b provided in parallel with each other along a passage of gas to be treated. In the discharge section, a discharge electrode 34 is constructed with a plate 31 extending in an intermediate portion between dust collecting electrodes 30a and 30b and needle pieces 33a and 33b fixed on a gas inflow side and gas outflow side, respectively, of the plate 31 by means of clasps 32a and 32b. The needle pieces 33a are embedded at a predetermined pitch along an end portion on the gas inflow side of the plate 31, and the pointed ends thereof extend toward the gas inflow side. Further, the needle pieces 33b are embedded at a predetermined pitch along an end portion on the gas outflow side of the plate 31, and the end portions thereof extend toward the gas outflow side.
In an electrostatic precipitator thus constructed, when a high voltage at which a discharge electrode 34 becomes a negative electrode is applied between the dust collecting electrodes 30a and 30b and the discharge electrode 34, corona discharges as shown with dotted lines are generated from the pointed ends of the needle pieces 33a and 33b toward the dust collecting electrodes 30a and 30b. As against the above, when gas to be treated containing dust flows as shown with an arrow mark, the greater part of the dust passing through a corona discharge area is charged negative.
Thus, a charged zone is formed in the portion where corona discharge is generated, and the dust charged in this charged zone is absorbed by the dust collecting electrodes 30a and 30b by means of the high electric field produced between the dust collecting electrodes 30a and 30b and the discharge electrode 34, and collected on the surfaces of these dust collecting electrodes 30a and 30b.
FIG. 8 shows an electrostatic precipitator which has been invented by the inventor of the present invention and put on the market. This electrostatic precipitator is composed of a discharge section 38 in which a discharge rod 36 where needle pieces 35 are embedded and hollow metallic rods 37 are installed collectively and a dust collecting section 40 in which hollow metallic rods 39 are installed collectively along the discharge section 38. Thus, in the electrostatic precipitator thus constructed, intense corona discharge is generated from the pointed ends of respective needle pieces 35 toward the dust collecting section 40. Further, due to the fact that the dust collecting section 40 is composed of an aggregate of hollow metallic rods 39, the surface area is increased on the whole and the dust collecting efficiency is improved.
Further, it is strongly demanded in recent years to remove bacteria while fitting an electrostatic precipitator to an air conditioner. In this case, it is desired to collect almost all the dust and miscellaneous bacteria contained in the gas to be treated which passes through the electrostatic precipitator.
However, when the dust and miscellaneous bacteria contained in the gas to be treated are in large quantities and the load is heavy, the demanded quantity cannot be satisfied in point of the dust collecting efficiency by the construction in the first conventional example (shown in FIG. 7) in which the dust collecting electrode and the discharge electrode are provided in parallel with each other with respect to the passage of the gas to be treated. For the purpose of improving the dust collecting efficiency, it is also possible to install the electrostatic precipitator having the structure shown in FIG. 6 while connecting it in a row to the passage of the gas to be treated. In this case, however, the distance from an inlet port to an exhaust port of the gas to be treated becomes lengthy, and the electrostatic precipitator becomes large in size, thus making it difficult to install it. The same is applied to the second conventional example (shown in FIG. 8).
Further, in a construction in which a dust collecting electrode and a discharge electrode are provided in parallel with each other with respect to a passage of the gas to be treated as in the past, reversely charged particles generated in a trace quantity with respect to the generating quantity of charged particles generated when the gas to be treated passes through the charged zone stick to the discharge electrode. As a result, the pointed end portion of the discharge electrode is thickened so as to hinder corona discharge, thus lowering the dust collecting efficiency. Thus, a hammering device giving an impact to the discharge electrode is required for removing reversely charged particles which have stuck to the discharge electrode. However, complete insulation is required for the hammering device since a high voltage is applied to the discharge electrode side, and installation of the hammering device is attended with complexity.
Further, a conventional electrostatic precipitator is provided with a hammering device for giving an impact to the dust collecting electrode and the discharge electrode in the passage of the gas to be treated in order to remove charged particles which have stuck to the dust collecting electrode and reversely charged particles which have stuck to the discharge electrode, but, in this case, the dust contained in the gas to be treated causes deterioration of the hammering device, which produces a difficult point in the maintenance aspect.